1. Field of the Invention
The invention relates in general to touch system, and more particularly, to a technique for enhancing the accuracy of sensing results for a border region of a touch panel.
2. Description of the Related Art
Operating interfaces of recent electronic products have become more and more user-friendly and intuitive as technology advances. For example, via a touch screen, a user can directly operate programs as well as input messages/texts/patterns with fingers or a stylus; in this way, it is much easier to convey demands than operating via traditional input devices such as a keyboard or buttons. In practice, a touch screen usually comprises a touch sensing panel and a display device disposed at the back of the touch sensing panel. According to a position of a touch on the touch sensing panel and a currently displayed image on the display device, an electronic device determines an intention of the touch to execute corresponding operations.
Current capacitive touch control techniques are in general categorized into self-capacitive and mutual-capacitive types. Self-capacitive touch panel, featuring a single electrode structure of a simpler fabrication process and low costs, prevails in entry-level electronic devices.
FIG. 1 shows an example of a self-capacitive touch panel. In a sensing region 100 demarcated by dotted lines, multiple electrodes (e.g., electrodes 11, 12, 14, 15 and 17) having equal widths and each appearing similar to a right-angle triangle are disposed. Due to costly sensors for detecting capacitance changes in the electrodes, current touch panels are frequently designed to have multiple electrodes share one sensor. As shown in FIG. 1, the electrodes 11 and 12 are coupled to a first upper sensor 13, and the electrodes 14 and 15 are coupled to a first lower sensor 16. In other words, rather than a capacitance change respectively corresponding to the electrodes 11 and 12, the capacitance change detected by the first upper sensor 13 is a sum of capacitance changes occurring at the electrodes 11 and 12. In FIG. 1, the capacitance changes detected by a 2*N number of sensors (an N number of upper sensors and an N number of lower sensors, each of which has a denotation and serves as an ith sensor, where i=1 to 2N) are transmitted to a controller (not shown) for the controller to determine an occurring user touch. The controller may calculate an x-coordinate along an X direction according to the equation below:
                    x        =                                            ∑                              i                =                1                                            2                ⁢                N                                      ⁢                          (                                                C                  i                  *                                ⁢                                  X                  i                                            )                                                          ∑                              i                =                1                                            2                ⁢                                                                  ⁢                N                                      ⁢                          C              i                                                          (        1        )            
In the above equation, i represents an integral index between 1 and 2N, Ci represents the capacitance change detected at the ith sensor, and Xi represents coordinates of a common centroid of electrodes coupled to the ith sensor. Taking the first upper sensor 13 as an example, the coordinates of the corresponding centroid Xi is a position of the common centroid of the two electrodes 11 and 12 (between the electrodes 11 and 12).
The touch panel in FIG. 1 faces a challenge of a remarkable error between sensing results of two left and right border regions. Reasons behind such occurrence are described below with reference to FIGS. 2 and 3 again depicting the electrodes 11, 12, 14, 15 and 17 in FIG. 1.
When a user touch occurs at a position represented by a dotted circle 21 in FIG. 2, only the electrodes 11 and 14 are affected. Thus, a noticeable error is incurred from calculating the x-coordinate based on the capacitance change detected by the first upper sensor 13 and the first lower sensor 16. More specifically, although the capacitance change detected by the first upper sensor 13 mostly comes from the electrode 11, instead of a centroid of the electrode 11, the controller nevertheless regards a position (denoted as P1) of a common centroid of the electrodes 11 and 12 as the position at which the capacitance change detected by the first upper sensor 13 occurs. Similarly, although the capacitance change detected by the first lower sensor 16 mostly comes from the electrode 14, instead of a centroid of the electrode 14, the controller nonetheless regards a position (denoted as P2) of a common centroid of the electrodes 14 and 15 as the position at which the capacitance change detected by the first lower sensor 16 occurs. Consequently, the x-coordinate calculated is apparently deviated to the right of the actual position of the circle 21.
Referring to FIG. 3, assuming that the circle 21 is not located at a border position of the sensing region 100, a left half of the circle 21 theoretically triggers another electrode 31 (physically non-existent, represented by dotted lines), thus providing a capacitance change that deviates the x-coordinate to the left (closer to real X-coordinate of the circle 21 than the x-coordinate). In other words, in a border region, due to the lack of a balancing value possibly contributed by the virtual electrode 31 as well as great distances from the centroids P1 and P2 to the real X-coordinate, the x-coordinate calculated by the controller may contain a remarkable error.
The above detection error at a border region much likely causes a misjudgment on an intention of a user touch to lead an incorrect operation result. Yet, discarding the left and right borders as a sacrifice for preventing the above issue, hardware costs are wasted.